The present invention relates to a fusing apparatus, as used in electrostatographic printing, such as xerographic printing or copying, and methods of operating thereof.
In electrostatographic printing, commonly known as xerographic or printing or copying, an important process step is known as xe2x80x9cfusing.xe2x80x9d In the fusing step of the xerographic process, dry marking material, such as toner, which has been placed in imagewise fashion on an imaging substrate, such as a sheet of paper, is subjected to heat and/or pressure in order to melt or otherwise fuse the toner permanently on the substrate. In this way, durable, non-smudging images are rendered on the substrates.
Currently, the most common design of a fusing apparatus as used in commercial printers includes two rolls, typically called a fuser roll and a pressure roll, forming a nip therebetween for the passage of the substrate therethrough. Typically, the fuser roll further includes, disposed on the interior thereof, one or more heating elements, which radiate heat in response to a current being passed therethrough. The heat from the heating elements passes through the surface of the fuser roll, which in turn contacts the side of the substrate having the image to be fused, so that a combination of heat and pressure successfully fuses the image.
In more sophisticated designs of a fusing apparatus, provision can be made to take into account the fact that sheets of different sizes may be passed through the fusing apparatus, ranging from postcard-sized sheets to sheets which extend the full length of the rolls. Further, it is known to control the heating element or elements inside the fuser roll to take into account the fact that a sheet of a particular size is being fed through the nip. When a relatively large sheet is passed through the nip, it is desirable to have an even distribution of heat along the length of the fuser roll, while when a smaller sheet is passed, it is desirable to radiate heat only along the portion of the fuser roll corresponding to the sheet, so that the system as a whole does not overheat.
Another design consideration which has recently become important in the office equipment industry is the avoidance of xe2x80x9cflickerxe2x80x9d with regard to a power system associated with the printing apparatus. xe2x80x9cAnti-flickerxe2x80x9d mandates, which basically require that the alternating current consumption of the machine as a whole does not affect the behavior of other equipment, such as fluorescent lighting, within the same building, are of particular concern in Europe and developing countries.
U.S. Pat. No. 4,301,359 discloses a fusing apparatus in which thermal sensors are located symmetrically relative to a midpoint along the length of a fuser roll, in order to take into account a profile of heat distribution along the fuser roll.
U.S. Pat. No. 4,309,591 discloses a fusing apparatus in which the heating elements are controlled to take into account the thermal expansion of at least one roll.
U.S. Pat. No. 5,300,996 discloses, at FIG. 5 thereof, a fuser roll which includes, among other features, two parallel heating elements.
U.S. Pat. No. 5,497,218 discloses a fuser roll in which a first heating element distributes heat substantially along the entire fuser roll, and a second heating element provides heat only over a portion of the length of the fuser roll.
U.S. Pat. No. 5,826,152 discloses a fuser roll in which the heating elements are disposed within a hollow cylindrical tube inside the roll. Each heating element is independently controllable.
U.S. Pat. No. 5,899,599 discloses a fuser roll in which there are provided two parallel heating elements.
U.S. Pat. No. 6,008,829 discloses, at FIG. 2 thereof, a fuser roll in which one heating element radiates heat mainly toward the middle of the fuser roll, while a second heating element radiates heat mainly at the ends of the fuser roll.
According to one aspect of the present invention, there is provided a method of operating a xerographic fusing apparatus, the apparatus having a first heating element and a second heating element, comprising the steps of incrementally changing an amount of power applied to the first heating element; and incrementally changing an amount of power applied to the second heating element outside of a predetermined time window relative to incrementally changing the amount of power applied to the first heating element.
According to another aspect of the present invention, there is provided a method of operating a xerographic fusing apparatus, the apparatus having a first heating element and a second heating element. When increasing power applied to the first heating element and second heating element, the first heating element and second heating element are caused to be connected in series. When the fusing apparatus is in a running condition, the first heating element and second heating element are caused to be not connected in series.